The Poisonous Brother
by AShinyLemon
Summary: Senkai Namikaze, the daughter of the Fourth Hokage, the container of the Nine Tailed Fox, and a hero to the village. A bright, warm, caring person, who seems to get along with everyone. Naruto Namikaze, the brilliant, anti-social and, to some, evil, brother. He's dedicated his life to ensuring that his sister succeeds and is happy- no matter the cost. (Fem!Sasuke)


_Ah here we are again. This will be a brand new universe, which I created (sort of) in my two old one shots. In this universe, Naruto is NOT the Nine Tails Host. His parents survive due to the sacrifice of the Third Hokage. His sister, Senkai, holds the Kyuubi. In this fanfic, Naruto will not be godlike. He will, at his max, be Low S Rank. His specialty is going to be strategy- plans, traps, ambushs, that sort of thing._

 _Expect: OOC, Character Death, Major Canon deviation after a certain point._

Debts must be repaid- Normal talking

 _Be it friend or foe-_ Thinking

 **I always repay them.-** Demon speaking/Shouting

Outfit time!

If you are confused about costumes, you can search them up, as the main characters outfits will be primarily from other media, which I will indicate.

I do not own Naruto, or any media referenced/used in this fanfiction. All media and material belong to their respective owners.

 _October 10_ _th_

"Happy birthday you two!" Naruto Uzumaki and Senkai Uzumaki were bombarded with cries of Happy birthday as they walked into the living area of the Namikaze estate. They were the twin children of Minato Namikaze and Kushina Uzumaki. However, they were not your average children. Naruto possessed a mind quite similar to that of a Nara. It was countered by his cold and dark personality. Senaki, meanwhile, was bright and bubbly, and she warmed up the room whenever she walked in. The two twins could not be more different, yet there were no problems. They cared for each other deeply, and if one was around, you could be sure that the other was nearby.

The father of the twins, Minato Namikaze, was the 4th Hokage of Konohagakure no Sato. He was nearly killed on October 10th eleven years ago when his children were born and his wife's seal broke. Kushina Uzumaki hailed from the proud Uzumaki Clan, which was wiped out by the combined might of three villages. She was selected to hold the Kyuubi no Kitsune, a feat only Uzumaki were capable of. However, the downside of having a female container was that their seals would be highly unstable during childbirth.

The Kyuubi broke free on that dreadful night, and it took everything the village had to keep him down long enough for Minato to form a plan. He had intended to use the reaper death seal to give up his life and seal the Kyuubi into one of his children. He was interrupted when the former third Hokage, Sarutobi Hiruzen, knocked him out and performed the sealing himself. He gave up his life so that Minato's twins would not be raised without a father. With Minato's survival, he was able to rapidly rush Kushina to a hospital to get her the medical treatment she needed. This ensured that both parents would live to raise their children.

"C'mon Naruto, go out there. Make some friends for once!" Senkai said, prodding her brother in the arm. "I'm fine Senkai. I have you and our parents. I don't need anyone else." Naruto said. He didn't like socializing much. He found people to be loud and irritating, especially those who didn't think like him. He had few exceptions to this rule, and he didn't intend to change anytime soon. "You sound mighty emo right now brother." Senkai said, pouting. "Wow. That hurts, right here Senkai-chan." Naruto said, pointing to his chest. "Naruto, Senkai, come to the living room. It's time for cake!" Senkai cheered and Naruto smirked. The two stood up and walked into the living room, Senkai chatting with various guests and friends and Naruto ignoring everyone who tried to talk to him.

"Ahh, if it isn't my two favorite gakis. How ya doing?" Jiraiya said. He rubbed both of their heads and they both blushed. "Please don't touch me Jiraiya-san. I don't know where your hands have been." Naruto said, and Jiraiya had a look of fake outrage on his face. "Hey, I keep clean! It should be you I'm worrying about! You are that age now, aren't you?" Naruto sputtered a bit as he tried to formulate a reply. "H-hey, isn't it a bit weird to be thinking of your godson like that?" Now Jiraiya was trying to come up with a reply when Tsunade walked over. "Stop screwing with the old perv and give me a hug you two." Senkai and Naruto rushed forward to hug Tsunade. "So, 11. You guys are going to be starting the academy soon, aren't you?" Tsunade said, letting them go.

The two twins nodded. "I can't wait and start my path to being Hokage!" Senkai said. "That's great Senkai-chan. Never lose that enthusiasm" Tsunade said. "Alright! Gather round the table, and bring the birthday kids!" Kushina said, and everyone went around the table.

Ten minutes later, the guests were all enjoying cake. Senkai was tearing into her presents with gusto, cake all over her face. Naruto was sitting in a corner eating his cake calmly watching his sister with a smile on his face. "Hello Naruto-kun. May I sit here?" a voice said. Naruto looked up to see Itachi Uchiha, an ANBU captain. Naruto nodded and Itachi sat down next to him. "Itachi-san, I heard you yourself have a younger brother." Itachi nodded. "He's the most precious thing in the world to me. I would do anything for him." He said, and Naruto looked over at Senkai again. "I'd do the same for my sister." Itachi then pulled out a package and handed it to Naruto. "This is for you." Naruto took it and nodded his head. "Thank you, Itachi-san." Itachi bowed before walking over to the other guests.

Later, after the party had died down, only the Namikaze family and their close friends remained. "Kakashi, what did I tell you about reading Jiraiya's crap in here!" Kushina yelled, and both Kakashi and Jiraiya got defensive. "It's not crap! It's a beautiful piece of literature!" Kakashi said, and Jiraiya high fived him. "Thank you! Someone understands!" Naruto and Senkai were laughing as Kushina started chasing them around with her sword. "Kakashi has a point, those books aren't half bad." Naruto said, and Tsunade heard him. "What? You read that filth!" Everyone stopped. "Jiraiya…you corrupted my son with your books?" Kushina said, and Jiraiya paled. "Now..Kushina…he was the one who asked to see them…"

Naruto frowned. "No, as I recall, you said it was a book about true love." Kushina summoned two chakra chains and wrapped them around Jiraiya. "Jiraiya, I think it's time for your punishment." Jiraiya instantly had a nosebleed. "Woah." Said Kakashi, and was knocked out by Tsunade. Jiraiya was then thrown out of the house by Kushina using her chains.

As the two twins prepared for bed, they were talking excitedly. "Naruto, what do you think the academy is going to be like? Are we gonna learn super powerful jutsu? Epic taijutsu moves?" Naruto smiled at Senkai's expectations. "It's more than likely going to be history and small, basic jutsu along with ninja tool training. We're kids, don't expect so much." Senkai pouted and turned around. "Buzzkill." Naruto smiled and walked over to his bed. "C'mon, we need to sleep." Senkai smiled and got into her bed. "Hey Naruto, promise me something." Naruto turned over to her. "What is it?" Senkai was quiet for a second before she began speaking. "Promise me that, no matter what, you'll always be there for me. " Naruto laughed a bit. "You're my precious sister. Of course, I'll always be there for you. Through anything." Senkai smiled and went to sleep.

 _TIMESKIP_

This had been a long time coming. Naruto and Senkai were finally ready to take the final exams to graduate the academy. "Naruto Namikaze, please enter." Naruto looked over to his sister, who smiled and nodded. "Knock em dead bro!" she said. Naruto smiled and entered the room. Iruka pointed to a desk for Naruto to sit at. "Alright, we'll begin with the written portion of the exam." He said, and handed Naruto a paper. The questions were rather simple, or so Naruto thought. He handed in the test and Iruka nodded. "Alright, now, henge into our Hokage." Naruto did a hand sign and was covered in smoke. When it dispersed, he was the spitting image of his father. "Alright, now, replace yourself with this log." Iruka said, placing the log in front of him. Naruto did another hand sign and suddenly he was where the log used to be. "Finally, perform a clone jutsu for me." Naruto performed the jutsu and was awarded full marks. "Good work, here's your hitai-ate." Naruto was handed a headband with a dark green cloth. He nodded and left the room.

"Senkai Namikaze, please enter." Iruka called out, and he nodded towards Senkai. "Good luck." She jumped up excitedly and practically ran into the room.

Later, she walked out with tears in her eyes. Naruto immediately rushed over to her. "What happened?" he asked, grabbing her by the shoulders. "I…I failed." She said. "You failed? But how? We went over everything for the test yesterday!" Naruto said, shaking her a bit. "I-it was the bushin. I couldn't make one that looked good…" she said, not being able to look her brother in the eye. "There has to be something we can do. Did you ask Iruka-san or Mizuki-san about any other alternate tests?" Naruto said. Senkai shook her head. "Mizuki-sensei did say that he wanted to talk to me about something though." Naruto pulled out a cloth and wiped her tears. "Alright, I want you to go to him and see what he wanted to talk to you about. Hopefully, it's some sort of retest." Senkai nodded and started walking to the academy.

 _One Hour Later_

Naruto was sitting down on a rock outside the academy, reading a book, when Iruka appeared next to him. "Naruto, have you seen your sister? There's something I need to ask her." Naruto looked up. "No, she said that Mizuki-san wanted to speak with her, so she left about an hour ago. Come to think of it, they've been talking for an unusual amount of time.." Naruto stood up. "Iruka-san, why do you think Senkai failed at producing a proper bushin? She certainly has the chakra reserves for it, and her control, while it needs work, should be adequate enough for her to make at least one. There has to be some outside influence.."

Iruka frowned. ' _So, he doesn't know? I'd have figured Hokage-sama would have told his own children about the fox..'_ "I have no idea, Naruto-san. However, it is urgent I find your sister. Would you accompany me in searching for her? I think you'd make the process a bit easier." Naruto nodded, and the two ninja went off in search of Senkai.

"ITS YOU! YOU'RE THE NINE TAILED DEMON FOX THAT ATTACKED OUR VILLAGE AND KILLED SO MANY!" Mizuki shouted, pointing at Senkai. "Wh-what do you mean? I'm not the nine-tailed fox…" Mizuki laughed. "Haven't you ever wondered exactly why some people look at you strange? Why they're reluctant to be around you? It's because you're the fox! Hokage-sama, as powerful as he is, couldn't defeat it, so he sealed it into one of his children!" Iruka and Naruto jumped next to Senkai. "That's not true, and you know it Mizuki." Iruka said, looking at him. He had a giant scroll in his hand, which could only mean one thing. "You tricked Senkai into stealing the Forbidden Scroll? Are you mad?" Iruka said.

"Of course! My master wants this scroll, and I can't afford to fail him. I'll bring this to him, kill the demon fox and be seen as a hero!" Naruto threw several kunai at him. "You're obviously an imbecile, thinking that's what will happen. Let me tell you exactly where you went wrong in your little plan!" He then charged at Mizuki, kicking him in the leg. "You first assumed the Hokage would just let his daughter take the scroll to some random stranger!" He jumped above Mizuki and kicked him in the back of the head, causing him to fall to the ground. "Then, you thought that by killing the DAUGHTER OF THE MOST POWERFUL NINJA ALIVE that you'd be seen as a hero?" Naruto kicked the scroll out of Mizukis hand towards Iruka, who caught it. "You're an idiot and a fool, and a disgrace to both the leaf village and the shinobi world as a whole."

Mizuki however, grinned. "That's great kid. Real genius analysis but.." He jumped up and grabbed Naruto by the neck. "Did you forget I'm a chunin? You're nothing but a fly to me, and I'll swat you like one!" He said, punching Naruto in the stomach. He then stabbed him with a kunai and threw him at Iruka. "Naruto!" Iruka yelled out, catching him, not seeing the explosive tag that was on his back. He dropped the scroll, which Mizuki quickly grabbed and jumped back. "I'll kill all of you and make my escape!" Mizuki yelled, running towards the border of the forest. Iruka quickly ripped the tag off and threw it on a nearby tree, which exploded. "Damn, he's hurt bad. Senkai, don't let him get away! Alert the ANBU an-" he looked up to see Senkai had vanished. ' _No, she's going off to face him by herself! She'll be killed!"_

Suddenly, several ANBU appeared next to him. "Iruka-san, have you spotted the traitor?" Iruka nodded. "He ran towards the edge of this forest. Genin Naruto Namikaze engaged him and was critically wounded. He needs medical attention now!" one of the ANBU nodded and took Naruto away with a shushin. "What about the other sibling, where is Senkai Namikaze?" Iruka grimaced. "Pursuing the traitor." He said, and the ANBU nodded. The ANBU nodded to his squadmates. "We'll go after them. Stay here, Iruka-san." They vanished, leaving Iruka there. ' _There is no way I'm abandoning my students!'_ He sought off after the ANBU.

"If it isn't the fox. Come to avenge your pathetic brother?" Mizuki said, pulling out another kunai. "I wont let you get away! Not only did you hurt my brother, but you're betraying the village!" Senkai said, rushing towards him. "It seems your brother has all the smarts in the family, huh kid?" Mizuki said, vanishing. ' _What? Where did he go?'_ suddenly, a giant shuriken was racing towards her. ' _No! he tricked me again!'_ As she prepared to meet her end, suddenly, blood sprayed on her face. Someone had jumped in front of her. "I-Iruka-sensei!" she said, looking at the scarred chunin. "Heh, looks like I got here in time…" he said, falling to the ground. "Iruka-sensei!" Senkai said, pulling out the shuriken. "Hah! Sacrificing yourself for a demon? So pathetic Iruka!" Iruka looked at Mizuki. He grabbed Senkai's arm, and pulled himself up. "Pathetic? What's pathetic…is that you think she's a demon.." He pulled out a scroll and unsealed a kunai. Mizuki got into a defensive stance, but relented a bit when he saw Iruka simply hold it up. "Is this kunai a sealing scroll, Mizuki?" Mizuki laughed.

"How much blood did you lose Iruka? Of course it's not a sealing scroll!" Iruka started laughing. "I'm..glad you recognized that. So how can you sit here and call Senkai a demon?" Mizuki frowned. "Don't make me laugh Iruka! Look at her face! Those whisker marks aren't natural! There's no way she isn't a demon. You should be supporting me on this! The demon killed those you loved!" Iruka's face fell into a frown. "You're right. The Demon did kill those I loved. I've always hated that damn demon for what it did." Iruka turned to Senkai. "However…Senkai is not the demon. She is a hardworking student, who always strives to do her best, despite her limitations…" Iruka turned around again.

"That's why..Thats why I have no problem giving my life for her!" He charged at Mizuki, who knocked him back. "If you're so determined to die here, then I'll make that happen!" he then threw more kunai at Iruka, who blocked a few. One of the Kunai found its mark in his leg, however. "And you're supposed to be a chunin instructor. Pathetic!" Mizuki said, not paying attention to the sudden red glow in the corner of his eye. "I..wont let you.. **hurt** **Iruka-sensei!** " Senkai shouted, running at Mizuki. " ?" he said, before being slammed into a tree. Suddenly, hundreds of Senkai's appeared around him, surrounding him. "H..how!" he shouted. Senkai smirked. " **I had some time to read the scroll. I saw this interesting jutsu that I thought would impress you enough to let me pass..but I think I'll just kill you with it!** " Mizuki saw all the clones of Senkai pull out kunais. "W-wait! If you let me go.. I'll give you the scroll! And leave! I'll never come back, I swear!" Senkai laughed. " **You hurt those important to me, and broke my trust. You're going to pay!** " As the clones prepared to murder Mizuki, they were suddenly dispelled. "Genin Namikaze, that's enough." A voice said.

A Weasel masked ANBU suddenly appeared next to her. The red cloak vanished as Senkai looked up. "Why ANBU-san? I thought we were supposed to execute traitors?" The ANBU looked at her. "We need to find out who he was working for. No mere chunin would come up with this kind of plan. There are other forces at play here, forces Hokage-sama wants us to look into."

"Whatever you say, Weasel-san." Senkai said, before stepping away from Mizuki. The ANBU retrieved the scroll and put it on his back. "Squad, take him to the Torture and Interrogation unit. I will return the scroll and Genin Namikaze to her father." The ANBU nodded and shushinned away with Mizuki. "Ah, ANBU-san, technically I'm not a genin, as I did not pass my test.." The ANBU looked at her. "As an ANBU, it's well within my rights to provide a field promotion in the event of outstanding performances. And, a mere academy student who is capable of taking on an academy instructor is worthy of the rank genin."

The two arrived at the Hokage's office to see Naruto being tended to by his mother. "Ow! Couldn't Tsunade-san do this?" he said, as his mother pricked him on accident. "Oh stop whining! A little stab wound didn't kill anyone!" Kushina said, looking at him. "There are SEVERAL cases in history that beg to differ mom!" Naruto said, as he was pricked again. "Hokage-sama, the scroll and traitor have both been retrieved." The weasel masked ANBU said. Minato nodded. "Senkai, are you alright?" Senkai nodded. "Mizuki-san said some things to me dad. Things about me being the nine tailed fox, and all that…" Minato looked to his wife. "Senkai…what Mizuki said..it isn't true. You aren't the nine tailed fox." Senkai looked relieved. "You are merely it's container." Minato said, releasing a breath he had held. "You are the thing that keeps the fox at bay, preventing it from getting out and killing hundreds. You're a hero, Senkai." Senkai smiled. She was a hero? Sweet!

Naruto snapped his fingers. "That might explain why she couldn't form a proper bushin. Her chakra is harder to control due to the foreign influence of the fox! OW!" he said, as he was pricked again. "I'm almost done, calm down!" Kushina said. The ANBU nodded. "That would be a good assumption to make, Naruto-san. Demonic chakra is different from regular chakra." Minato whistled. "Where'd you come up with that Naruto?" Naruto pointed at his mother. "You told me that she had crappy control when she was younger, and she used to be the demon host. So, I sort of took a leap as to why Senkai couldn't form a proper bushin." Kushina frowned. "I did not have crappy control! I had uh… needs improvement control, at the worst!" The Namikaze family laughed at this, while the ANBU excused himself.

"Senkai, Naruto, what you heard tonight, is an S-Class secret. No one can know what Senkai contains. It would invite other countries to kidnap or kill her." Naruto and Senkai nodded. "Now, I think a celebration is in order, for our two new genins!" Minato said. "Who's up for ramen?" Senkai and Kushina cheered, while Naruto just gave a thumbs up. "Great, we'll go after Kushina finishes with Naruto. "Dad, ramen for breakfast is kind of unhealthy, don't you think?" Naruto said. "OW! That one was on purpose!" he shouted, while Kushina chuckled. "Maybe."

 _Ok, how was that? I stopped working on this and came back to it waaaay later than I intended to. Now, as for my other stories, this is what im thinking._

 _-A Star Wars story_

 _-A Yandere-Sim. Story_

 _-Another Naruto Story_

 _So tell me which one you'd want to see first! I'd really appreciate a review telling me how you felt about this! I'll be updating Ghost Stories soon (possibly tomorrow)!_

 _See ya next time!_


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